1. Field of the Invention
The present invention relates to an apparatus for supporting an operator at the time of radiotherapy treatment.
2. Description of the Related Art
In radiotherapy treatment typified by external X-ray radiotherapy treatment, before the treatment, an irradiation plan (the direction and the dose of radiation to an affected region) is made on a patient image. On the basis of the irradiation plan, irradiation of the patient is performed. However, at present, there is no means for confirming whether irradiation is actually performed to the patient with the planned position and dose or not. Even if insufficient irradiation of an affected region or excessive irradiation of a normal tissue occurs, it is not noticed. In some cases, using a phantom and an X-ray detector prior to irradiation, whether planned irradiation can be performed or not is confirmed. However, it is difficult to place a patient in a position according to the irradiation plan, on a bed different from a phantom which is easily portable and whose position can be freely adjusted. The confirmation prior to radiation does not completely assure the planned irradiation of the patient.
A technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 05-156526 is to detect scattered X-rays in an X-rayed subject and to obtain a cross-sectional image of the subject. The characteristic of the technique is that a scan is performed with a pencil beam and a three-dimensional scattering radiation image of the subject is reconstructed. That is, the technique assumes only the pencil beam but is not directed to obtain a scattering radiation image of a region through which a beam having a limited width passes (a spatial distribution of dose of a therapeutic beam), which is used in X-ray therapy. Since forward scattering is dominant in the scattering in a subject of a therapeutic beam (a few MeV) having high energy, when a detector is disposed in the incident X-ray direction, it is difficult to distinguish scattering radiation and penetrated radiation from each other. A correction process is therefore necessary for detection of scattering radiation.
Amid mounting social concern over medical errors, also in radiotherapy treatment, excessive irradiation of a patient has been reported and has become an issue. It is predicted that recording of the “fact” of medical acts performed such as a region in a patient and an irradiation dose is becoming more and more important. In the field of external X-ray radiotherapy treatment, attempts to irradiate an affected region more precisely are being made such as a method of irradiation so as to synchronize and trace motion of a tumor in a patient caused by breathing or the like, a method of collimating a therapeutic X-ray beam in accordance with the shape of a tumor and irradiating the tumor with the beam, and the like. The object of the precise irradiation is to concentrate the dose to an affected region. Therefore, if the therapeutic X-ray beam is off from the irradiation target, normal tissue is considerably damaged. As the irradiation is becoming more precise, it is becoming more important to check whether the irradiation is performed as planned.